This has happened to me twice already when accessing a Realm via my Nintendo Switch as well. In my case, I entered the Realm, built a bridge over a river, exited out, and then later, logged back in and I was back where I was before, bridge no longer built. It felt like a groundhog day loop.
This too also didn't happen until after I updated to 1.13.0 on my Switch, and my wife had updated the Realm to 1.13.0 as well.
Now that you mention it... I did pluck a map off the wall and check it to get it to update and reflect the changes I had made. The house I built in the village has a town map set up on the wall, and I would check it to see it update after making specific changes. Namely, I was looking for it to show this bridge over a river I had built. The map updated fine, but later, when I logged in, time had flowed backward to before the bridge was built. I hope whatever is causing this and the Bell issue gets fixed and soon. I want to get this town in order!